Computer telephony integration

ABSTRACT

When a terminating call is forwarded by a CTI-enabled switch to an off-switch destination, the associated CTI controller is notified of the delivery of that call and in response the controller records that destination number as busy and invokes a call back when free request in respect of the destination number. When a notification is received at the CTI-enabled switch that the destination number has become free, the controller is notified, and in response records the destination number as free. The CTI-enabled switch may comprise a switch in combination with a telephony card.

This application is the US national phase of international applicationPCT/GB011/01283 filed 23 Mar. 2001 which designated the U.S.

BACKGROUND

1. Technical Field

This invention relates to the use of a computer for controlling theoperation of a telephony system, such use is known in the art ascomputer telephony integration (CTI), and the systems employing suchcontrol are known as CTI systems.

2. Description of Related Art

As a general background, the reader will find examples of such CTIsystems disclosed in the articles “Introduction to Computer TelephonyIntegration”, by A. Catchpole, G. Crook, and D. Chesterman, BritishTelecommunications Engineering, Vol. 14, July 1995; “Computer TelephonyIntegration—The Meridian Norstar”, by A. Catchpole, BritishTelecommunications Engineering, Vol. 14, Oct. 1995; “Computer TelephonyIntegration—The Meridian 1 PBX”, by P. Johnson, A. Catchpole, and L.Booton, British Telecommunications Engineering, Vol. 15, July 1996;“Callscape Computer Telephony Integration for the Small Business”, by G.Hillson, G. Hardcastle, and M. Allington, British TelecommunicationsEngineering, Vol. 15, January 1997, and “Call Centres—Doing Business byTelephone” by M. Bonner, British Telecommunications Engineering, Vol.13, July 1994.

BRIEF SUMMARY OF EXEMPLARY NON-LIMITING EMBODIMENTS

According to a first aspect of the present invention there is provided amethod of operating a computer telephony integration (CTI) systemcomprising a CTI-enabled switching means, and an associated CTIcontroller coupled to the CTI-enabled switching means via a CTIsignalling link, the method comprising the steps of:

-   -   responding to receipt of a call terminating at the CTI-enabled        switching means by        -   delivering that terminating call to a destination network            termination, and        -   sending to the CTI controller signalling data of that call            comprising at least the directory number of that destination            network termination;    -   notifying the CTI controller of an answer condition with respect        to that destination network termination; and,    -   in response to that notification, sending from the CTI        controller to the CTI-enabled switching means a command for        invoking a call back when free facility in respect of that        destination directory number.

Preferably, there are included the steps of:

-   -   further responding at the CTI controller to that notification of        an answer condition by notifying the CTI controller of the        receipt at the CTI-enabled switching means of an indication,        generated in accordance with that facility as the result of that        destination network termination being subsequently deemed free        by that facility; and    -   in response to that notification of the receipt of an        indication, changing the recorded current status of that        destination network termination to free.

The step of notifying the CTI controller may comprise forwarding to theCTI controller the indication received at the CTI-enabled switchingmeans.

The CTI controller may further respond to that notification of an answercondition by recording the current status of that destination directorynumber as busy.

A method of this first aspect may include the steps of:

-   -   providing to that facility a number for use as a destination        directory number of a call to be made in accordance with that        facility as the result of that destination network termination        being subsequently deemed free by that facility;    -   notifying the CTI controller of the receipt at the CTI-enabled        switching means of a said call made in accordance with that        facility;    -   in response to that notification of the receipt of a said call        made in accordance with that facility, recording the current        status of that destination network termination as free.

There may be included the further step of responding to thatnotification of the receipt of a said call by sending from the CTIcontroller to the CTI-enabled switching means a command for cancellingthat call back when free facility in respect of that destinationdirectory number.

The step of responding to receipt of a call terminating at theCTI-enabled switching means may comprise:

-   -   extending that terminating call to the CTI controller via a        first channel of a transmission link; determining said        destination network termination;    -   making an originating call to that destination directory number        from the CTI controller via a second channel of the transmission        link; and    -   joining the terminating call and the originating call at the CTI        controller.

According to a first aspect of the present invention there is provided acomputer telephony integration (CTI) system comprising a CTI-enabledswitching means, and an associated CTI controller coupled to theCTI-enabled switching means via a CTI signalling link:

-   the CTI-enabled switching means being arranged    -   to respond to receipt of a call terminating at the CTI-enabled        switching means by        -   delivering that terminating call to a destination network            termination, and        -   sending to the CTI controller signalling data of that call            comprising at        -   least the directory number of that destination network            termination; and    -   to notify the CTI controller of an answer condition with respect        to that destination network termination; and,-   the CTI controller being arranged to respond to that notification,    by sending to the CTI-enabled switching means a command for invoking    a call back when free facility in respect of that destination    directory number.

The CTI-enabled switching means may be further arranged to notify theCTI controller of the receipt at the CTI-enabled switching means of anindication, generated in accordance with that facility as the result ofthat destination network termination being subsequently deemed free bythat facility; and

-   the CTI controller may be further arranged to respond to that    notification of the receipt of an indication by changing the    recorded current status of that destination network termination to    free.

The CTI-enabled switching means may be arranged to forward to the CTIcontroller the indication received at the CTI-enabled switching means.

The CTI controller may be further arranged to respond to thatnotification of an answer condition by recording the current status ofthat destination directory number as busy.

There may be included means for providing to that facility a number foruse as a destination directory number of a call to be made in accordancewith that facility as the result of that destination network terminationbeing subsequently deemed free by that facility; and the CTI-enabledswitching means may be arranged to notify the CTI controller of thereceipt at the CTI-enabled switching means of a said call made inaccordance with that facility; and the CTI controller may be arranged torespond to that notification of the receipt of a said call made inaccordance with that facility by recording the current status of thatdestination network termination as free.

Preferably, the CTI controller is further arranged to respond to thatnotification of the receipt of a said call by sending to the CTI-enabledswitching means a command for cancelling that call back when freefacility in respect of that destination directory number.

The CTI-enabled switching means may be arranged to respond to receipt ofthe terminating call by extending that terminating call to the CTIcontroller via a first channel of a transmission link; and the CTIcontroller may be arranged to determine said destination networktermination, to make an originating call to that destination directorynumber from the CTI controller via a second channel of the transmissionlink, and to join the terminating call and the originating call at theCTI controller.

BRIEF DESCRIPTION OF THE DRAWINGS

Specific embodiments of the present invention will now be described byway of example with reference to the drawings, in which:

FIG. 1 shows a first embodiment of a system of the present invention;

FIG. 2 shows a second embodiment of a system of the present invention;and

FIG. 3 shows a third embodiment of a system of the present invention.

DETAILED DESCRIPTION OF EXEMPLARY NON-LIMITING EMBODIMENTS

Acronyns used in the following description.

-   BT British Telecommunications public limited company-   CBWF Call Back When Free-   CLC Calling-Called Line Category-   CLI Calling Line Identity-   CTI Computer Telephony Integration-   DA destination address-   DN directory number-   DNIS Dialled Number Identification Service number-   ISRM Initial Service Request Message-   OLI Originating Line Identity-   PBX Private Branch Exchange-   PCM Pulse Code Modulation-   PSTN Public Switched Telephone Network-   SIC Service Indicator Code

In FIG. 1 there is shown a first embodiment of a CTI system comprising aCTI-enabled PBX 10 connected to its associated CTI controller 12, alsocalled a CTI server, via a CTI link 14 and a 2.048 Mbit/s 32-channel PCMtransmission link 16. The CTI-enabled PBX 10 is also connected to a PSTN18 via a 2.048 Mbit/s 32-channel PCM transmission link 20, and to a PBX22 via a 2.048 Mbit/s 32-channel PCM transmission link 24.

The transmission links 16, 20 and 24 are each terminated at theCTI-enabled PBX 10 by respective primary rate cards 26, 28 and 30; thetransmission link 16 is terminated at the CTI controller 12 by a primaryrate card 32; and the transmission link 24 is terminated at the PBX 22by a primary rate card 34. The CTI-enabled PBX 10 and the PBX 22 areenabled to send and receive signalling messages via the transmissionlink 24 using a signalling system known in the art as Digital PrivateNetwork Signalling System No.1 (DPNSS1) and described in the documentBTNR 188 available from BT.

The CTI link 14 is terminated at the CTI-enabled PBX 10 by a CTIinterface card 36 and at the CTI controller 12 by a CTI interface card38. The CTI interface cards 36 and 38 operate in accordance with a CTIprotocol known as Computer Supported Telecommunications Applications(CSTA). There are a number of proprietary CTI protocols, e.g. MeridianLink from Northern Telecom, and several “open”, or proposed standard,CTI protocols, including CSTA, but the performance of the presentinvention is not dependent upon the use of any particular CTI protocol.

The CTI-enabled PBX 10 and the PBX 22 are both connected to a respectiveplurality of telephones, also referred to as extensions, correspondingto ONs within their respective numbering ranges, of which, forconvenience, only one telephone 40 is shown connected to the CTI-enabledPBX 10, and only one telephone 42 is shown connected to the PBX 22.Herein, telephones are also referred to as network terminations.

The operation of the CTI-enabled PBX 10 and its associated CTIcontroller 12 will now be described with reference to a call made from auser A having a telephone 44 connected via a local exchange (not shown)to the PSTN 18, to a user B associated with the telephone 40.

In this embodiment the CTI controller 12 is responsible for determiningwhere the call is delivered. Therefore, on receipt of the call via thetransmission link 20, the CTI-enabled PBX 10 will first send thesignalling data, i.e. the CLI and the DNIS, of that call to the CTIcontroller 12 and await a delivery instruction. Assuming firstly thatuser B wants incoming calls delivered to his telephone 40 and has notinvoked, for example, a Call Forward facility, the CTI controller 12will respond with a delivery instruction for delivery to the telephone40, and the CTI-enabled PBX 10 will respond by causing telephone 40 toring.

The CTI-enabled PBX 10 is programmed to report to the CTI controller 12the various stages of its call processing, i.e. the telephony states.Thus, when telephone 40 is caused to ring, a corresponding message issent to the CTI controller 12 which records that the state of telephone40 has gone from Free to Ringing. When user B answers that call, the CTIcontroller 12 responds to the next message, for that call, from theCTI-enabled PBX 10 by changing the recorded state from Ringing to Busy,and when user B goes on-hook at the end of that call, the CTI-enabledPBX 10 responds to the next message, for that call, from the CTI-enabledPBX 10 by changing the recorded state from Busy to Free.

The present invention enables the CTI controller 12 to maintain its calllog for situations where the CTI-enabled PBX 10 has delivered the callto a remote PBX, for example the PBX 22, which, in the most likelysituation, is not CTI-enabled and programmed to monitor and report onthe telephony states. For the following description, the CTI-enabled PBX10 is also referred to as the Originating PBX, and the PBX 22 isreferred to as the Terminating PBX.

Before describing the present invention, it will be instructive for thereader to understand how in known CTI systems the CTI controller 12 doesnot know when a call delivered off-switch, i.e. sent to a TerminatingPBX, goes from Busy to Free. Assume, therefore, that user B wants hiscalls delivered to telephone 42 in the conventional CTI system.

The CTI controller 12 will respond to the incoming call from A with adelivery instruction for delivery to the telephone 42, and theCTI-enabled PBX 10 will act as the Originating PBX and respond bysending an Initial Service Request Message (ISRM) to the TerminatingPBX. The Terminating PBX will communicate with the Originating PBX byconventional Call Set Up messages in accordance with DPNSS1, and up tothe time that user B answers at telephone 42, the Originating PBX hascontrol of the call (in case there is no answer and the Originating PBXhas to take alternative action) and sends appropriate messages to theCTI controller 12. Thus, when user B answers, the CTI controller 12records that user B is Busy at telephone 42.

The Originating PBX responds to the message from the Terminating PBXindicating an answer at telephone 42 by connecting that incoming call toa transmission channel in the transmission link 24 and ceasingmonitoring. In other words, the Originating PBX has no further interestin monitoring that call. Thus, when user B goes on hook and theTerminating PBX signals this to the Originating PBX, that connectionwill be taken down, but no message will be sent to the CTI controller12, and the recorded state of telephone 42 (user B) will remain at Busy,although it is actually Free.

The present invention is concerned with actions after the OriginatingPBX has forwarded the call to the Terminating PBX, and user B hasanswered the call at telephone 42.

Up to this point, the CTI controller 12 receives the conventionalmessages from the Originating PBX, and progresses through recording thestatus of user B as Ringing, and subsequently as Busy. The last messageof this stage is an answer message from the Terminating PBX, containingin Delivered Directory Number field the directory number to which thecall has been delivered, in this case the directory number of telephone42, i.e. its extension number, and the Originating PBX responds bysending a corresponding reporting message to the CTI controller 12.

According to the present invention, the CTI controller 12 additionallyresponds to receipt of this corresponding reporting message byinstructing the Originating PBX to make a “Call Back When Free—Request”in respect of the directory number of that message, i.e. telephone 42.

In this embodiment, the Originating PBX responds to that instruction toinitiate a CBWF request by selecting for use as an OLI an available oneof a pool of “reserved” extension numbers, i.e. numbers for which thereare no physical line cards and telephones; sending, by means of aVirtual Call, a corresponding message, “ISRM-CBWF: REQUEST”, to theTerminating PBX; and storing that CBWF message. The Terminating PBX alsostores that CBWF message, marked as waiting for telephone 42 to becomefree. This message has a message type field containing “ISRM(C)”; an SICfield containing “TELE”; an OLI field containing the selected number; asignalling type field containing “CLC-ORD”; a CBWF type field containing“CBWF-R”; and a destination address (DA) field containing the directorynumber of telephone 42.

In variants, the CTI controller 12 performs the selection of the“reserved” number to be used as the OLI, and passes that to theOriginating PBX with the instruction.

As part of the known CBWF facility, the Terminating PBX will send aClear Request Message (CRM) having a message type field containing“CRM”; a Clearing Clause (CC) type field containing “CC: Acknowledge”; aCLI field containing the number of telephone 42; and a State ofDestination (SOD) field containing “SOD B”, and in response theOriginating PBX will return a Clear Indication Message (CIM), which isidentical to that CRM except that its message type field contains “CIM”.

When user B finishes the call and puts the telephone 42 on-hook, theTerminating PBX detects this and, if telephone 42 is still free after atimeout of three seconds in which user B may make a follow on call,generates a “CALL BACK WHEN FREE—FREE NOTIFICATION” message “, which itsends to the Originating PBX. This message is similar to the “ISRM-CBWF:REQUEST”, but differs in that the CLC field contains “CLC-NET” toindicate that network signalling is being used, and in that the CBWFtype field contains “CBWF-FN”. The Terminating PBX also blocks telephone42.

When the Originating PBX receives this “CBWF-FN” message, it returns anAcknowledgement CRM, to which the Terminating PBX replies with anAcknowledgement CIM. The Originating PBX then proceeds to generate thenext message of the CBWF sequence, namely a “CALL BACK WHEN FREE—CALLSETUP”, and to send it to the Terminating PBX. This message is similarto the “ISRM-CBWF: REQUEST”, but differs in that the CLC field contains“CLC-ORD” to indicate that ordinary signalling is to be used, and inthat the CBWF type field contains “CBWF-CSU”. The Terminating PBX isprogrammed to withhold ringing from the telephone 42 at this stage.

On receipt of this CBWF-CSU message, the Terminating PBX responds with aNumber Acknowledge Message (NAM). As “reserved” extension numbers haveno actual line cards and telephones, their SOD is permanently set toFree, so the Originating PBX will respond to receipt of that NAM byapplying a calling signal to the “originating extension” for this CBWFsituation, i.e. the selected extension number, and reporting to the CTIcontroller 12 that an incoming call had been received for the selectedextension from telephone 42. The CTI controller 12 now changes therecorded state of telephone 42 from Busy to Free.

The Originating PBX will wait for a timeout of sixteen seconds, cancelthe stored CBWF request message, and send a CRM containing “CC-REJECT”,causing the stored CBWF request message to be cancelled at theTerminating PBX. In variants, the CTI controller 12 further responds toreceipt of that report by immediately instructing the Originating PBX totreat the timeout as having matured.

In another embodiment of the present invention shown in FIG. 2, theCTI-enabled PBX 10 is replaced by PBX 50, which is not enabled for CTIoperation, together with a telephony card 52 mounted in a computer (notshown) and coupled to the PBX 50 via a 2.048 Mbit/s 32 channel PCMtransmission link 56 having primary rate interface cards (not shown) ateach end. The signalling link 14 from the CTI controller 12 is connectedto the telephony card 52. In this embodiment the computer and the CTIcontroller 12 are disposed in different locations, but in variants theCTI controller 12 is constituted by a program running on that computer.The PBX 50 and the telephony card 52 together constitute a CTI-enabledswitching system of the present invention.

Upon receipt of an incoming call from network termination 44, the PBX 50effectively terminates that call on the telephony card 52 using a firstof the channels of the transmission link 56 to send a DPNSS1 signallingmessage to the telephony card 52 reporting the arrival of that call. Thetelephony card 52 sends a corresponding CSTA message via the signallinglink 14 to the CTI controller 12, which determines the actualdestination for that call, i.e. whether the call is to be delivered toan extension of the PBX 50 or forwarded to an extension of a remote PBX,for example the PBX 22.

In this embodiment, because the PBX 50 is not enabled for direct CTIcontrol, the CTI controller 12 originates a call from the telephony card52 to the actual destination using a second channel of the transmissionlink 56, and, upon receiving notification of answer at the destinationtelephone, commands the telephony card 52 to connect the first andsecond channels, and records the state of that destination extension asBusy. The PBX 50 detects, in known manner, that the incoming call fromnetwork termination 44 is now extended out to a remote PBX and performsroute optimisation to connect the incoming call directly to thatoutgoing call, and to drop the “tromboned” section to and from thetelephony card 52. The CTI controller 12 has thus lost its directvisibility of that call.

In similar manner to the first embodiment, the CTI controller 12 sendsvia the CSTA signalling link 14 an instruction to initiate aCBWF-REQUEST. The telephony card 52 responds by selecting a “reserved”extension number for use as the OLI and sending an “ISRM-CBWF: REQUEST”message to the PBX 50, which stores that message and sends it on to theremote PBX, as described above.

When the destination extension becomes free, the remote PBX will send a“CALL BACK WHEN FREE—FREE NOTIFICATION” message to the PBX 50, whichresponds by sending a call setup message (CBWF-CSU) to the remote PBX.

The remote PBX makes a call to that “reserved” extension number, whichwill be received at the telephony card 52, and its arrival reported tothe CTI controller 12. The CTI controller 12 will change the recordedstate of the original call from Busy to Free, and instruct the PBX 50 tocancel the CBWF-REQUEST. The PBX 50 cancels its stored request, andsends to the remote PBX a CRM containing “CC-REJECT”, causing thecorresponding stored CBWF request message to be cancelled at the remotePBX.

In FIG. 3 there is shown a further embodiment of a CTI system similar tothe embodiment of FIG. 1 but differing in that the transmission link 16is omitted and in that the CTI-enabled PBX 10′ (Originating PBX) of thisembodiment has a modified control program.

The operation of the Originating PBX and its associated CTI controller12 will now be described with reference to a call made from the user Ato the user B associated with the telephone 40.

As in the first embodiment, the Originating PBX will first send thesignalling data, i.e. the CLI and the DNIS, of that call to the CTIcontroller 12, and await a delivery instruction.

In the case that user B wants incoming calls forwarded to the telephone42, the CTI controller 12 will provide the delivery instruction fordelivery to the telephone 42, and, in response to being notified of thesubsequent receipt of the answer message at the Originating PBX, willissue the instruction to initiate a CBWF request. The CTI controller 12will have recorded, as before, the telephony status of the telephone 42,identified by its directory number, as now being Busy.

The Originating PBX of this embodiment is arranged to respond toinstructions from the CTI controller 12 to initiate CBWF requests bysending, by means of a Virtual Call, the corresponding message,“ISRM-CBWF: REQUEST”, to the Terminating PBX; and storing that CBWFrequest message. In the normal manner, the Terminating PBX also storesthat CBWF request message, marked as waiting for telephone 42 to becomefree. The OLI field of this “ISRM-CBWF: REQUEST” contains all nullcharacters since, as is described in detail below, the CBWF facility, asinvoked by the CTI controller 12 for the purposes of the presentinvention, does not progress to the “CALL SET-UP” stage. On receipt ofthis request message, the Terminating PBX does not examine the OLIfield, and its operation is not affected by the null characters.

As part of the known CBWF facility, the Terminating PBX will send aClear Request Message (CRM) having a message type field containing“CRM”; a Clearing Clause (CC) type field containing “CC: Acknowledge”; aCLI field containing the number of telephone 42; and a State ofDestination (SOD) field containing “SOD B”, and in response theOriginating PBX will return a Clear Indication Message (CIM), which isidentical to that CRM except that its message type field contains “CIM”.

When user B finishes the call and puts the telephone 42 on-hook, theTerminating PBX detects this and, if telephone 42 is still free after atimeout of three seconds in which user B may make a follow on call,generates the “CALL BACK WHEN FREE—FREE NOTIFICATION” message “, whichit sends to the Originating PBX.

When the Originating PBX receives this “CBWF-FN” message, it notifiesthe CTI controller 12 of that receipt by forwarding that message to theCTI controller 12, and the CTI controller 12 responds by changing therecorded telephony state of the telephone 42 from Busy to Free. In avariant, the Originating PBX sends instead a corresponding “FREENOTIFICATION” message to the CTI controller 12 in respect of thedirectory number of the telephone 42, i.e. the contents of the DA fieldof the received message.

The Originating PBX also cancels the stored CBWF request message forthat directory number, and sends to the Terminating PBX a CRM containing“CC REJECT”, causing the corresponding stored CBWF request message to becancelled at the Terminating PBX. In a variant, the Originating PBXcancels the stored CBWF request message for that directory number inresponse to a command from the CTI controller 12.

The principle of operation of this further embodiment is applicable tothe above arrangement of the combination of the PBX 50, which is notenabled for CTI operation, together with the telephony card 52.

Whereas the specific embodiments described above are based on a switchin the form of a PBX, it will be appreciated that the present inventionembraces other forms of switching function. For example, the switch canbe a public network switch, such as a Nortel DMS100 switch which is usedin known CTI arrangements in conjunction with a CompuCall CTIcontroller; and other forms of switching function include switches knownas Automatic Call Distributor (ACD), Interactive Voice Response (IVR),and server PBX. Furthermore, the type of switching is not limited to anyone form, and, in addition to switched circuit technology, includesAsynchronous Transfer Mode (ATM) switching, and Voice over InternetProtocol (VoIP) switching. With regard to this last form of switching,the switch can be a PBX having an Internet Card, or it can be a generalpurpose computer, e.g. one running Windows NT, having an Internet card,e.g. a Dialogic Internet card, and in this latter case the CTIcontroller function is provided by a program running in the computer,rather than in a separate controller. Furthermore, the telephones at theworkstations can connect to their respective clients via Internet phonejacks, and in an alternative arrangement telephony can be provided forthe user via a sound card in his client.

Thus, it can be seen that in general the present invention can beimplemented in any computer controlled switch, by means of a suitablecontrolling program.

In the above specific embodiments, the called user is an individualperson who normally works at a workstation. It will be appreciated thata DNIS need not correspond to an individual person, but may relate to adepartment or group, or a specific function within a company.Furthermore, more than one DNIS can correspond to such a function.

Similarly, the present invention includes caller identities other thanthe abovementioned CLI. These include a cell identity when the caller isusing a mobile telephone, an alphanumeric string, an Internet Protocoladdress, and “null” information, e.g. where a caller has withheld hisCLI.

It will also be appreciated that the term CTI, although originating fromthe computer control of voice telephony, is not limited to voicecommunications and includes other types of communications, e.g.videotelephony, and multimedia.

In the above described specific embodiments, the CTI server controller12 sends a message to the computer for each of the store 48 members. Inthis way, the called user will get a screen pop including a “calleridentity”, i.e. details of the caller, immediately or after a definedtime. The caller identity being typically the CLI (or a null identity ifCLI is withheld) or equivalent, and any translation to a name for thecaller (or Unknown if no translation is found). Each active computer,other than the called user, receives the message, but does not displaythe caller identity until the workgroup member clicks on the calleduser's icon. In a variant, only the called user is sent a messageincluding the caller identity, and the other active computers receive amessage containing only the called user identity. In this case, when aworkgroup member clicks on the called user's icon, a request is sentfrom his computer to the CTI controller 12 for a return messagecontaining the caller identity.

Furthermore, whereas the abovedescribed specific embodiments are thirdparty CTI arrangements, the skilled person will appreciate that thepresent invention is also applicable to first party CTI arrangements.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise”, “comprising” and thelike are to be construed in an inclusive as opposed to an exclusive orexhaustive sense; that is to say, in the sense of “including, but notlimited to”.

1. A method of operating a computer telephony integration (CTI) systemcomprising a CTI-enabled switch, and an associated CTI controllercoupled to the CTI-enabled switch via a CTI signalling link, the methodenabling the CTI controller to maintain a call log of the CTI controllerwhen a call is delivered off-switch by said CTI-enabled switch, themethod comprising the steps of: responding to receipt of a callterminating at the CTI-enabled switch, the call being initially directedto an on-switch destination network termination, by: delivering thereceived call initially directed to the on-switch destination networktermination from the CTI-enabled switch to an off-switch destinationnetwork termination, and sending to the CTI controller signalling dataof the call comprising at least a directory number of the off-switchdestination network termination; notifying the CTI controller of ananswer condition with respect to the off-switch destination networktermination; and in response to notifying the CTI controller, sendingfrom the CTI controller to the CTI-enabled switch a command for invokinga call back when free facility in respect of the directory number of theoff-switch destination network termination, wherein responses to saidcommand received by said CTI-enabled switch in respect of saidoff-switch destination network termination enable the CTI controller todetermine when the call is delivered off-switch via a remote switch andto update a telephony state of said off-switch destination networktermination in the call log.
 2. A method as in claim 1, wherein saidoff-switch destination network termination is connected to said CTIsystem via the remote switch and wherein the remote switch is notCTI-enabled.
 3. A method as in claim 1, wherein the CTI-enabled switchis the CTI-enabled switch of the on-switch destination networktermination to which said call is initially directed, and saidoff-switch destination network termination is a forwarded destinationnetwork termination determined by a user of said on-switch destinationnetwork termination.
 4. A method as in claim 1, wherein said response tosaid command includes the steps of: further responding at the CTIcontroller to the notification of an answer condition by notifying theCTI controller of the receipt at the CTI-enabled switch of anindication, generated in accordance with the facility as the result ofthe off-switch destination network termination being subsequently deemedfree by the facility; and in response to that notification of thereceipt of an indication, updating the telephony state of saidoff-switch destination network termination in the call log by changing arecorded current status of the off-switch destination networktermination to free.
 5. A method as in claim 4, wherein the step ofnotifying the CTI controller comprises forwarding to the CTI controllerthe indication received at the CTI-enabled switch.
 6. A method as inclaim 1, wherein the CTI controller further responds to the notificationof an answer condition by recording a current status of the directorynumber of the off-switch destination network termination in the call logas busy.
 7. A method as in claim 1 further comprising the steps of:providing to the facility a number for use as a destination directorynumber of a call to be made in accordance with the facility as theresult of the off-switch destination network termination beingsubsequently deemed free by the facility; notifying the CTI controllerof the receipt at the CTI-enabled switch of said call made in accordancewith the facility; in response to the notification of the receipt ofsaid call made in accordance with said facility, recording a currentstatus of the off-switch destination network termination is the call logas free.
 8. A method as in claim 7 further comprising the step ofresponding to the notification of the receipt of said call by sendingfrom the CTI controller to the CTI-enabled switch a command forcancelling the call back when free facility in respect of the off-switchdestination directory number.
 9. A method as in claim 6, wherein thestep of responding to receipt of the call terminating at the CTI-enabledswitch comprises: extending the terminating call to the CTI controllervia a first channel of a transmission link; determining said off-switchdestination network termination; making an originating call to thedestination directory number from the CTI controller via a secondchannel of the transmission link; and joining the terminating call andthe originating call at the CTI controller.
 10. A computer telephonyintegration (CTI) system comprising: a CTI-enabled switch; and anassociated CTI controller coupled to the CTI-enabled switch via a CTIsignalling link: the CTI-enabled switch being arranged: to respond toreceipt of a call terminating at the CTI-enabled switch, the call beinginitially directed to an on-switch destination network termination, by:delivering the received call which is initially directed to theon-switch destination network and terminates at the CTI-enabled switchfrom the CTI-enabled switch to an off-switch destination networktermination, and sending to the CTI controller signalling data of thecall comprising at least a directory number of the off-switchdestination network termination; and to notify the CTI controller of ananswer condition with respect to the off-switch destination networktermination; and the CTI controller being arranged to respond to thenotification of the answer condition by sending to the CTI-enabledswitch a command for invoking a call back when free facility in respectof the directory number of the off-switch destination networktermination, wherein responses to said command received by saidCTI-enabled switch in respect of said off-switch destination networktermination enable the CTI controller to determine when the call isdelivered off-switch via a remote switch and to update a telephony stateof said off-switch destination network termination.
 11. A system as inclaim 10, wherein the CTI-enabled switch is further arranged to notifythe CTI controller of the receipt at the CTI-enabled switch of anindication generated in accordance with the facility as the result ofthe off-switch destination network termination being subsequently deemedfree by the facility; and the CTI controller is further arranged torespond to the notification of the receipt of an indication by changinga recorded current status of the off-switch destination networktermination to free.
 12. A system as in claim 10, wherein theCTI-enabled switch is arranged to forward to the CTI controller theindication received at the CTI-enabled switch.
 13. A system as in claim10, wherein the CTI controller is further arranged to respond to thenotification of an answer condition by recording a current status of theoff-switch destination directory number as busy.
 14. A system as inclaim 10, wherein the facility is provided a number for use as anoff-switch destination directory number of a call to be made inaccordance with the facility as the result of the off-switch destinationnetwork termination being subsequently deemed free by the facility; andthe CTI-enabled switch is arranged to notify the CTI controller of thereceipt at the CTI-enabled switch of a call made in accordance with thefacility; and the CTI controller is arranged to respond to thenotification of the receipt of said call made in accordance with thefacility by recording a current status of the off-switch destinationnetwork termination as free.
 15. A system as in claim 13, wherein theCTI controller is further arranged to respond to the notification of thereceipt of said call by sending to the CTI-enabled switch a command forcancelling the call back when free facility in respect of the off-switchdestination directory number.
 16. A system as in claim 13, wherein theCTI-enabled switch is arranged to respond to receipt of the terminatingcall by extending the terminating call to the CTI controller via a firstchannel of a transmission link; and the CTI controller is arranged todetermine said destination network termination, to make an originatingcall to the off-switch destination directory number from the CTIcontroller via a second channel of the transmission link, and to jointhe terminating call and the originating call at the CTI controller. 17.A system as in claim 10, wherein the remote switch is not CTI-enabled.18. A system as in claim 10, wherein the call initially directed to theon-switch destination network termination is delivered to the off-switchdestination network termination as determined by instructions of a userof the on-switch destination network termination.